Shunt balancing network for telegraph circuits



Nov.29, 1938. R, T. HAMLETT 2,138,675

v SHUNT BALANCING NET-WORK FOR TELEGRAPH CIRCUITS Filed Nox/f5, 1935 3 shets-sheei 1 /Ve talon/ hun t A ,BO/onc/'rlg' Network AIJac/C @vmjm Nov. 29, 1938.

R. T. HAMLETT SHUNT BALANCING NETWORK FOR TELEGRAPH CIRCUITS Filed Nov. 5, 1935 Anti-Inducon 5 Sheets-Sheet 2 @www Nov. 29, 1938. R, T, HAMLETT 4 2,138,675

SHUNT BALANCING NETWORK FOR TELEGRAPH CIRCUITS Filed NOV. 5, 1935 3 Sheets-Sheet 5 SW/TCHBOARD 7 171e mvv@ 4 7022er? ZT Hamle Patented Nov. 29, 1938 UNITED STATES PATENT OFFICE SHUNT BALANCING NETWORKYFOR TELE- GRAPH CIRCUITS Application November 5, 1935, Serial No. 48,401.

Claims.

This invention relates to signaling systems and more particularly to circuit arrangements for connecting duplex sets into composite telegraph and telephone circuits. l

When telegraph circuits are operated over the same wires which are being used for telephone communication, it is necessary to insert filters in the line for the purpose of removing the interfering voice frequency currents which are generated in certain parts of the telegraph apparatus. One of these filters is usually connected in series with a conductor from the telegraph set to the line wire of the composited circuit.

If the telegraph circuit is to be operated as a duplex line, it then becomes necessary to insert a compensating lter network in the artificial line to balance the characteristics of the line lter. This has been accomplished heretofore by inserting identical lter networks in series with the line and in series with the artificial line of the duplex set. In case a duplex line was to be composited with another line, it necessitated the disconnection of the artificial line from the telegraph set and the employment of an additional conductor from the head end of the articial line to the switch board.

The object of my invention is to provide an arrangement for eliminating the additional conductor heretofore required between the artificial line and the terminal switchboard in order to introduce a compensating lter network when connecting a duplex set into a composite circuit; to make such change without disturbing the regular switchboard termination of the duplex set, the switchboard jacks for terminating the composite apparatus being entirely independent of the duplex set; and to increase the flexibility of the entire composite arrangement so that it may be used on any duplex set and line wires which are regularly terminated in the switchboard.

My invention will be more clearly comprehended from the following detailed description in connection with the accompanying drawings,

in which- Figure 1 is a diagrammatic View showing the manner of connecting the compensating lter network in accordance with my invention;

Figure 2 illustrates the manner of introducing the Voice frequency eliminating lters in the line circuit and the compensating filter network in the artificial line at the switchboard in accordance with my invention;

Figure 3 shows the ordinary switchboard termination of a duplex telegraph set;

Figure 4 illustrates diagrammatically the manner in which the circuit connections must be changed tot insert the compensating lter network into the articial line and which requires an additional conductor between the head end of the articial line and the terminal switchboard; and

Figure 5 shows the switchboard connections required when said additional conductor is empl'oyed.

I have indicated in Fig. 3 the usual connections at the terminal switchboard of a duplex set. The telegraph set is connected to the main line through the tip contacts of the two jacks, IU and l2, while the conductor 5 from the head end of the artificial line is connectedV through the sleeve contacts of the jacks to the usual antiinduction network which connects the head end of the artificial lines of the various duplex sys- :tems at a terminal station for the purpose of :eliminating cross-lire between the lines. Such anti-induction networks are shown in U. S. Patent No. 1,560,540 and are described. in an larticle in the Bell System Technical Journal, July, 1926, beginning on page 418.

Now when a duplex set is to be embodied as a part of a composite telegraph and telephone circuit it is necessary to eliminate the voice frequency disturbing currents which are generated in certain parts of the telegraph apparatus. The anti-noise set or apex iilter 7, shunts out most of the disturbing frequencies due to the transmitter T. To eliminate the voice frequency current components generated in the main line relay by the vibratory movements of the armature, it is necessary to insert a line lter or line composite set 8 in the line. This necessitates the introduction of a corresponding compensating network 8a in the artificial line to balance the characteristics of the low pass filter 8 in the line. This has heretofore necessitated the disconnection of the terminal telegraph set from the head end of the artificial line at the point 6 and the laying of a special conductor 52L from the terminal switchboard to the head end of the artificial line which is usually a considerable distance, Another method which has been employed necessitated the introduction of a compensating network in series with the articial line at each telegraph set and switching means for removing the network from the circuit. I have indicated diagrammatically in Fig. 4, the changes which were necessitated when a duplex line shown in Fig. 3 was connected into a composited circuit. The composited circuit arrangement in which two duplex telegraph lines comprise the two legs of l nected across the two telegraph lines is familiar to every communication engineer and hence it is not necessary to include a complete diagram for purposes of illustration herein.

The switch connections at the terminal switchboard which were required in order to change the duplex line shown in Fig. 3, into the composited circuit of Fig. 4, were quite complicated, as indicated in Fig. 5. In addition to the two jack switches Hl and l2, four additional jack switches I3, I4, I5 and i6, together with their interconnecting conductors were required. Moreover, it was necessary to alter the connections of the main line and artificial line with the jack switches l and l2 in order to introduce the filter network 8 into the line and the compensating network 8 into the balancing artificial line by means of patching jack's and cords as will be observed by referring to Fig. 5.

For the purpose of greatly simplifying the circuit connections required to connect a duplex set into one leg of a composited circuit and to eliminate the additional conductor heretofore required, I have devised the arrangement disclosed in Figs. 1 and 2. Instead of inserting the compensating filter network in series with the artiiicial line, I connect the iilter compensating network Ba in shunt to the usual conductor 5 leading from the head of the articial line to the antiinduction network. The constants of this compensating shunt filter 8a viz: the values of the condenser C, the inductanice L and the resistance R, are so chosen that they closely approximate the impedance (at telegraph frequencies) of the low pass iilter network 8, introduced in series with the line connection of the telegraph set. A coil I1 may also be connected in series with the anti-induction lead in order to correct the antiinduction network when the shunt balancing net- -work is connected.

Referring to the switchboard connections in Fig. 2, it will be observed that by eliminating the special conductor 5a previously required, the terminal connections of both the line wire and the conductor 5 to the switches l and l2, remain Vunchanged when shifting an ordinary duplex set shown in Fig. 3, into a leg of a composite circuit as shown in Fig. 2. This makes it possible to use any duplex set (terminated as shown in Fig. 3) for composite service without making any 'changes on the set. The two jack switches i3 and I4 used for terminating the composite apparatus are entirely independentof the duplex set and the other jacks on the switchboard. The flexibility of the entire composite arrangement is thus greatly increased, since the composite apparatus may be used on any of the duplex sets and line wires which are regularly terminated in the switchboard.Y Y

The manner in which the telephone circuit is bridged across a pair of telegraph lines is well understood and requires no further illustrations.

l. In a signaling system employing a composite set comprising a pair of telegraph lines and a telephone circuit bridged across said lines, one of said lines being arranged for duplex operation, a low pass filter connected in said duplex line to eliminate interfering voice frequency components from the outgoing telegraph signals and means 2,138,675 Y f f for balancing the effect of said filter in the artificial line of said duplex line, comprising a. network connected in shunt to the articial line, said network having electrical constants closely approximating the 'constants of said filter, at telegraph frequencies.

2. In a signaling system having a duplex telegraph line forming one branch of a composite telegraph and telephone circuit, a filter network in said line operating to eliminate voice frequency switchboard provided with the usual jack switches having socket and plug elements, a duplex telegraph line having a conductor from the telegraph set and a conductor from the head end of the grounded artificial line terminated in the spring contacts of one switch socket of a pair of jack switches and having the main line and conductor to the usual anti-induction network terminated respectively at the spring contacts of the other switch socket of said pair, a low pass voice frequency iilter network having its terminals connected respectively to corresponding spring contacts of a second pair of switch sockets and a compensating lter network having one terminal grounded and the other terminal connected to the other spring contacts of said second pair of switch sockets, whereby said duplex line may form one branch of a composite set by inserting the plugs on the opposite ends of a pair of the usual 'connector cords into the corresponding sockets of said pairs Vof switches.

5. In a signaling system having a. plurality of duplex telegraph sets provided with the usual grounded artificial line and having a conductor from the usual anti-induction network connected to the head end of the artificial line, aterminal switchboard provided with jack switches having socket and Vplug elements, the telegraph set and said conductor connected to the articial line of the respective duplex lines terminating in the spring contacts of the socket elements of respective pairs of said switches and the corresponding telegraph lines and anti-induction conductors terminating in the spring'contacts of the other socket elements of said pairs and a plurality oi lsets of low pass line lters Vand corresponding compensating lter networks terminating in pairs of socket elements of said switchboard switches with said compensatingn filter networks 'connected between the head of the articial line and ground, whereby any duplex line may be readily adapted to form a leg of a composite set by inserting the plugs of the usual connector cords in the corresponding terminal sockets of a duplex line and the sockets of a filter set. 

